An image sharing service using the Internet is emerging. The image sharing service is a service in which a terminal unit (client terminal) of a participator uploads an image such as photo, picture or graphics to the server that stores the image to allow the participators to share the stored image. In the image sharing service, the participator can arbitrarily manipulate the image stored in the server with an operation from his or her own terminal unit. This image manipulation function was conventionally realized by installing a dedicated image processing program such as a helper application program, ActiveX (registered trademark) program or JavaApplet program into the terminal unit. That is, the participator downloads an image to be manipulated from the server to the terminal unit, an image processing program of the terminal unit executes a manipulation process on the image based on a drawing operation at the terminal unit, in response to the drawing operation, and the participator uploads the image having undergone the manipulation process to the server to restore it. However, with this conventional method, it was required to install the dedicated image processing program into the terminal unit, thereby discouraging broad use.
As a method for implementing an image manipulation process on the image sharing service using the functions of the WEB browser without installing the dedicated image processing program into the terminal unit, it is conceivable that the image processing program is prepared on the server side, a drawing operation is operated from the terminal unit, and the corresponding image manipulation process is executed with the image processing program on the server side. That is, the participator downloads an image to be manipulated from the server to the terminal unit and makes a drawing operation on the browser screen of the terminal unit, on which the image is displayed; the terminal unit adds the information required to execute the image manipulation process on the server in response to the drawing operation to an HTTP request as a parameter of the HTTP request and issues the HTTP request for the image having undergone the image manipulation process; the server receives this HTTP request, controls the image processing program based on the information included as the parameter in the request to execute the corresponding image manipulation process, and returns the image having undergone the manipulation process as a response to the HTTP request; and the terminal unit receives the image having undergone the manipulation process and updates the original image displayed on the browser screen with the image having undergone the manipulation process.
By the way, in executing the image manipulation process, it is required that the manipulation process result is reflected, following the drawing operation (movement, etc. of the cursor), on the screen of the terminal unit where the drawing operation is operated (i.e., the display image is modified successively with the progress of the drawing operation, such as the line is drawn along the position which the cursor passes on the screen, etc.). Updating the display in this way is generally called an echo back. In the drawing operation, if the response of echo back is slow, the manipulation process result is not promptly reflected to the display image on the screen where the drawing operation is operated, whereby the drawing operation can not be operated as desired, and is less convenient in use.
The slow response of echo back is problematical, especially in the drawing operation for modifying the image by means of the brush tool having a density representation. Herein, the “brush tool having a density representation” means a drawing tool for realizing the drawing in which the drawing density is varied in accordance with a manner of drawing operation of the pointing device (moving speed for moving the cursor while holding the mouse button down, the time of pressing and holding the mouse button with the cursor placed at one position, etc.), which is called as a pen tool, a brush tool, a paintbrush tool, or an air brush tool, for example. For example, the air brush tool produces the effect of spraying the ink, in which an ink spray image is drawn like a circle with predetermined largeness at the position of the mouse cursor by pressing the mouse button. The density distribution may be set such that the nearer to the center of the circle in operating the drawing, the higher the density is. And the drawing density can be gradually higher, depending on the time of pressing and holding the mouse button down at one position. Also, when moving the cursor while holding the mouse button down, the drawing is thinner if the moving speed is faster, or the drawing is denser if the moving speed is slower. Accordingly, if the manipulation process result (the image manipulated by the air brush) through the drawing operation of the air brush is not reflected promptly on the screen where the drawing operation is operated, the operator can not know how long the mouse button should continue being pressed, or how fast the mouse cursor has to be moved, and can not operate the drawing as desired. Accordingly, the faster response of the echo back is particularly important in the drawing operation for modifying the image by means of the brush tool having a density representation.